Study of the variable genome of Photobacterium damselaeacquisition of new metabolic traits, antimicrobial resistance and a novel virulence plasmid

Résumé

The two subspecies of Photobacterium damselae, namely subsp. damselae and subsp. piscicida, are pathogenic for diverse fish species of financial importance in marine aquaculture. In the present thesis we have characterized the variable genome in these two subspecies, which proved to be highly diverse. We have demonstrated that horizontal gene transfer has played a major role in the acquisition of the ability to metabolize sucrose, and in antimicrobial resistance in the subspecies damselae. Notably, this study has unveiled the existence of a novel, highly unstable virulence plasmid, encoding a Type III secretion system (T3SS) that is highly prevalent in the subspecies piscicida, and which constitutes a new virulence factor in this pathogen.